The invention relates to marine drive lower gearcases with a vertical drive shaft driving a horizontal propeller shaft in a torpedo housing and having a propeller mounted on the propeller shaft at the rear of the torpedo housing. The invention more particularly relates to an improved location for the drain plug which upon removal permits drainage of the lubricant in the lower gearcase.
A marine drive lower gearcase includes a torpedo housing with an internal cavity holding lubricant for lubricating the gears and bearings in the gearcase. A threaded drain plug is provided in a threaded bore through the torpedo housing near the nose thereof. The bore typically includes a counterbore to accommodate the enlarged head of a threaded member. The outer lip of the counterbore at the nose of the torpedo housing is on the exterior hydrodynamic surface of the torpedo shape along which water flows. The outer lip of the bore is a disruption in the hydrodynamic surface and causes cavitation burns on the torpedo housing and the propeller, i.e. blistered and removed paint on the torpedo housing exterior surface just aft of the plug hole bore, and pitting of the propeller. A further objection to the noted drain plug hole is the difficulty in machining same because it is difficult to hold a location on the eliptical surface of the torpedo.
The present invention addresses and solves the above noted problems in a simple, cost effective manner. In the present invention, the drain plug is mounted to the torpedo housing at a location away from the hydrodynamic surface of the latter to prevent cavitation burns on the torpedo housing and the propeller. The invention also aids in eliminating propeller ventilation.